I've heard a few times now "campaign X died because there were no good antagonist for the player characters". So I thought to myself "there are archetypes available for protagonists in a RPG campaign. What would antagonist archetypes look like?"

These are just some random musings on the subject to arrange my thoughts, so caveat emptor.

The Organization

The organization is big, powerful and faceless. It could utterly crush the protagonists - if it could catch them, or in fact, if it was even aware of them.

The organization could be a megacorp, an oppressive government, a world-spanning conspiracy, a ever-present crime ring, or the big and powerful slavers' guild. Whatever it is, it has several tiers or ranks; once the players penetrate the first layer, they face an even more powerful layer beyond.

Campaign style: Rebels

In Rebels, the protagonists are out to tear down the organization. They want to destroy its power base, take down its representatives or find out the big secret who would utterly expose the organization and make it vulnerable.

Campaign style: Fugitives

The protagonists are on the run from the organization. They have a McGuffin that it wants, or they know the terrible secret that the organization does not want exposed, or perhaps they just need to be made examples out of. It may even be that it merely thinks the protagonists have those things, when in fact they do not.

Campaign style: Dystrophy careers

The protagonists are in fact members of the organization, yet constantly threatened by it. This is a dystrophy where the supposed source of strength and support is in fact the nemesis.

Campaign style: Infiltrators

Similar to "Dystrophy careers" above, only here the protagonists have the ultimate goal of fighting the organization, which makes it slightly less dystropic.

The Puppet Master

Hidden mastermind threat. Has some great weakness or secret, so he cannot let himself be exposed. Strikes through agents, manipulations and conspiracies.

Campaign style: Monster of the Week

Degenerate case. The antagonist just sends out a new threat each time the previous one has been defeated.

Perhaps he is just testing the protagonists

Perhaps it is the fights he wants, instead of having the protagonists defeated

Resource strapped

Campaign style: Terrorized

Protagonists have something to defend against a shadowy opponent that can strike at any time.

The Wave

An enormous horde is coming, and the only thing standing between it and that which needs protecting, is the protagonists.

It might be a barbarian invasion, a demon incursion, or stray rag-tag bands of ex-soldiers turned bandits after the war ended.

Campaign Style: Buildup

It starts with just a few raindrops, indicating the downpour to follow. Isolated incidents that need investigating, but their frequency start to grow, and soon a terrible threat looms. Will the protagonists manage to reach their goal before the wave's main body enters, whether that goal is finding the solution that stops the wave in its track, managing to convince the general public to prepare and defend, or to simply evacuate that which is most precious to them?

Campaign Style: The Last Line of Defense

The protagonists are the only thing that stands between the world as we know it and total annihilation. Failure with their missions is not an option, since they are the only ones with the knowledge or the capabilities that keep the Wave at bay.

Campaign Style: The Seven Samurai

A small pocket of civiliazation needs to be defended from the encroaching wave, but its inhabitants are woefully inadequate at defending themselves; not only do they need to gain both confidence and training, but they need to be armed and defenses erected in preparation for the inevitable confrontation.

Campaing Style: The Growth of Corruption

Something unseen is turning perfectly ordinary people into threats, and it is spreading. It might be a disease that kills of the empathy part of the brain, turning people into murderous sociopaths, an outbreak of vampirism or zombie fever, or aliens planting their mind-control larvae into people.

This is the more paranoid variant of Buildup above.

The Competitors

With a competitor, the antagonist is not a threat to be eliminated once and for all, but an opponent that needs to be overcome again and again. The competition can be friendly or hostile, or even both. Allies may become competitors and vice versa without hard feelings.

Campaign style: Proselytizing

A series of antagonists that have to be overcome - and once defeated they become friends and allies. Perhaps they were made to see the error of their ways, perhaps they just realized your Kung-Fu was stronger than theirs and your way is thus the true one, or it is part of the knightly code, or they are mercenaries who realize what side the bread is buttered on.

Campaign style: The Big Race

Both protagonists and antagonists compete to accomplish a major undertaking first: Race around the world in an airship, build the first Calvorite spacecraft to reach the moon. The protagonists compete for resources, results and sympathy with the antagonists, and trickery and sabotage complicates the competition.

Campaign style: Changing Hands

An object of great importance keeps changing hands between the protagonists and the antagonists. It might be a white stone of purely symbolic nature, it might be the magic totem that ensures fertility of the village, or it might be the ring the controls the great Genie that fulfills wishes. It can be won in competitions, it may be stolen by stealth or trickery, or it might be fought over, but it never stays in one position long...

The Hunter

A single opponent is on the protagonists' tail, following them everywhere.

Campaign Style: The Exterminator

He's big, he's scary, he never gives up, and he'll definitively kill the protagonists if he ever catches them. In order to avoid him, they constantly have to be on the move, forcing them to meet new people and new situations - situations they have to solve in order to keep their trail as inconspicuous as possible. (See also Fugitives under Organization above).

Campaign Style: Wile E. Coyote

He's big, he's bumbling, he never gives up, and his inept attempts to "get even" with the protagonists are so embarrassing and self-destructive that the protagonists try to avoid this antagonist just to keep a little peace and avoid having to pick up the pieces. Unfortunately, this indestructible menace keep appearing, throwing things into chaos, upsetting the protagonist's plans, and making things plain unpredictable.

The Enigma

The antagonist moves by strange and hidden rules. The protagonists' challenge is to figure out what those rules are, enough to successfully interact with it and thus fulfill their goals.

Note that an Enigma antagonist might just as well be a setting as a persona.

Campaign Style: The Big Dumb Object

The BDO, or Big Dumb Object [1], is an enormous, strange artifact that needs to be entered and explored. Within are places that obey mysterious rules and do strange things for odd reasons. Perhaps their rules can be deciphered, and the object can be safely traversed. Perhaps...

Campaign Style: The Omnipotent Idiot Savant

An omnipotent being controls the protagonists' world. Perhaps they are trapped within a virtual world run by rogue AI, perhaps a new god awoke in the neighborhood, perhaps they make first contact with a much more advanced alien race. The problem is that the antagonist does not understand the protagonist, and needs to be taught to respect the protagonists and interact with them.

Campaign Style: The Rat Maze

An unknown and unfathomable antagonist has caught the protagonists, and as part of a cruel experiment they are forced through a series of enigmatic challenges that needs to be puzzled out in order to survive and make it out. If there is an exit to the maze...